Stable solution of an aluminum salt of a methyl silane triol



United States Patent STABLE SOLUTION OF AN ALUMINUM SALT OF A METHYL SILANE TRIOL Arnold Torkelson, Hoosick Falls, N. Y., assignor to General Electric Company, a corporation of New York No Drawing. Application May 27, 1952, Serial No. 290,318

4 Claims. (Cl. 106-487) This invention is concerned with aluminum salts of hydrocarbon-substituted silane triols having reduced alkalinity. More particularly, the object of this invention is the product formed by a process for reducing the pH of aqueous solutions of alkali-metal salts of hydrocarbonsubstituted silane triols which process comprises adding to the said solution a single aluminum salt in an amount sufficient to reduce the pH of the aforesaid alkali-metal salt.

Alkali-metal salts of hydrocarbon-substituted silane triols have been disclosed as being eminently useful for rendering various bodies water-repellent. The use of such alkali-metal salts for the aforesaid stated purpose is more particularly described in Krieble and Elliott Patent 2,507,200, issued May 9, 1950, and assigned to the same assignee as the present invention as Well as in the application of William S. Kather, Serial No. 290,313, filed concurrently herewith and assigned to the same assignee as the present invention. Additional uses of the aforesaid alkali-metal salts of hydrocarbon-substituted silane triols (hereinafter referred to as alkali-metal salts) are disclosed in Elliott and Krieble Patents 2,441,422 and 2,441,423. Generally, in treating materials such as textiles or paper with the alkali-metal salt, it is desirable to use the salts in the form of aqueous solutions in which to dip the textile or paper. Good water repellency is obtained on such sheet materials by merely drying the treated cloth whereby the carbon dioxide and moisture in the air form a mildly acidic environment which causes condensation of the alkali-metal salt to the hydrocarbon-substituted polysiloxane.

However, in employing these alkali-metal salts, it has been found that due to their highly basic characteristics, the pH of sodium salts of rnethylsilane triols being of the order of about 13 to 14, there is an undesirable Weakening of the textile or paper fibers when the treated cloth or paper is dried at elevated temperatures. Although fairly good water repellency is obtained on cotton cloth treated, for instance, with the sodium salt of methylsilane triol (sodium methyl siliconate) and thereafter air-dried and although cloth thus treated is not weakened to any great extent, air drying is impractical when applied to modern industrial cloth-treating practices and therefore it has become necessary to use elevated temperatures with the attendant disadvantages that the cloth is weakened and there is an undesirable reduction in the'degree of water repellency.

Attempts have been made to obviate the above-described disadvantages by neutralizing the dilute alkalimetal salt solutions with an acid and to use the neutral sols, for instance, methyl siliconic acid sols, to impart water repeliency to textiles. The objection to acid neutralization is twofold. First, neutralized solutions using acids as the neutralizing medium have been found ineffective in waterproofing textiles. Secondly, referring, for instance, to the alkali-metal salt of methylsilane triol, methyl siliconic acid sols are unstable and tend to precipitate after standing a short time. Often precipitation will start before neutralization is even complete.

I have now discovered that alkali-metal salts of hydrocarbon-substituted silane triols in the form of aqueous solutions can be readily neutralized to any degree desired down to a pH of about 6.8 to 7.0 by employing as the neutralizing agent a single aluminum salt in an amount sufiicient to give the desired degree of neutralization while at the same time maintaining the stability of the solution. The neutralized compositions thereby obtained are effective as Water repellents on various materials including textiles, paper, masonry, etc., and can be used for many applications without necessitating the use of elevated temperatures during drying operations.

The alkali-metal salt with which the present invention is concerned may be prepared from mono-organosilane triols or their condensation products and are described, for example, by Meads and Kipping, Journal of the Chemical Society, 105, page 679. The metallic salts can be prepared, for instance, by hydrolyzing derivatives of a monohydrocarbon-substituted silane containing three hydrolyzable radicals, for instance, halogen atoms, alkoxy radicals, etc., connected to silicon, recovering the hydrolysis products and dissolving these products in an aqueous solution of an alkali-metal hydroxide in such proportion that there is preferably, although not neces sarily, present at least one equivalent of base per silicon atom. Further directions for making the metallic salt may be found disclosed in the aforesaid Krieble and Elliott Patent 2,507,200. The resultant solution containing the soluble metallic salt is diluted to the desired concentration, with water or water-soluble alcohols, e. g., ethanol, etc., or both. The hydrolyzable monohydrocarhon-substituted silanes mentioned above and used in making the alkali-metal salt maybe considered as having the formula RSiXs Where R is a monovalent hydrocarbon radical, for example, alkyl (e. g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, decycl, etc.), aryl (e. g., phenyl naphthyl biphenyl etc.), aralkyl (e. g., benzyl, phenylethyl, etc.), alkaryl, (e. g., tolyl, xylyl, etc.), and substituted-hydrocarbon radicals in which the substituent is non-reactive with the hydrolyzable medium or with the inorganic base used to make the metallic salt. Such sbstituents are, for example, halogens, e. g., chlorine, bromine, fluorine, etc. In the above formula X may be a halogen, for instance, chlorine, bromine, fluorine, etc.; alkoxy, e. g., methoxy ethoxy, propoxy, etc., amino groups, e. g., the -NH2 grouping. Preferably, X is a halogen, particularly chlorme.

Among the inorganic bases which may be employed in making the alkali-metal salts may be mentioned, for example, potassium hydroxide, sodium hydroxide, cesium hydroxide, etc. 1

Generally, it is desirable when making the aqueous alkali-metal salt solution to obtain it in a concentrated form, for example, in concentrations of the order of about 20 to 50 per cent total solids content (alkali-metal salt) and thereafter dilute it with Water to the desired concentration applicable for the neutralization step. I have found that good results are obtained if the solution contains the alkali-metal salt of the hydrocarbonsubstituted silane triol on a Weight basis of less than 6 per cent organopolysiloxane calculated as RSiO1.s (e. g., CHsSiO1.5) where R is a monovalent hydrocarbon radical. The use of concentrations of less than 6 per cent organopolysiloxane permits obtaining solutions of the alkali-metal salt which are less alkaline and which are relatively quite stable. As the concentration exceeds the 6 per cent value described above, the stability of the neutralized solution decreases. It will, of course, be apparent to those skilled in the art that the scope of the inventionincludes smaller or larger concentrations of the alkali-metal salt in the'aqueous solution, provided one observes the precautions mentioned above.

The addition of small amounts of alcohols or ketones to the water solution of the alkali-metal salt enhances the stability of such solutions and lowers their freezing points. In this respect small amounts of alcohols, ketones or ethers are employed which are miscible with the water solution.

' The term single aluminum salt or aluminum salt employed hereinis intended to mean single aluminum salts, preferably soluble in water, but necessarily soluble inthe aqueous solution of the alkali-metal salt of the hydrocarbon-substituted silanetriol. Among such salts (hydrated or non-hydrated salts) may be mentioned, for instance, aluminum halides (e. g., aluminum chloride, aluminum bromide, etc.),' aluminum sulfate, aluminum nitrate, basic aluminum acetate, aluminum citrate, etc. The aluminum salts used in the present invention must be-capable of forming with the alkali-metal salt a waters'oluble, neutral (pH=7) or close to neutral salt. Thus, aluminum nitrate would form, e. g., sodium nitrate,'with the alkali-metal salt, aluminum sulfate would form, e. g., sodium sulfate with the alkali-metal salt, etc. Aluminum phosphate would not be satisfactory because in most concentrations in solution it would form a salt with the alkali-metal salt which would be only slightly less basic than the original alkali-metal salt. I have found that the simple aluminum salts are best for the purpose, and if one' employs complex aluminum salts, for example, alum, KAl(SO4)2, the stability of the neutralized solution is materially impaired so that there may be gelation and precipitation after addition of the complex aluminum salt.

It appears that the aluminum salts are unique for the purpose as' far as metallic salts in general are concerned. Thus, the use of iron salts, for instance, ferric nitrate, for neutralizing the solutions of the alkal-metalsalt, gives colored reaction products which are stable for only short periods of time, and because of the color involved, cannot be used in the wide range of applications for which the colorless reaction products obtained in the presently claimed invention can be used. The employment of metallic salts of tin, for instance, stannic chloride, gives neutralized compositions which have very poor stability and obviously have little. utility. Zinc salts, for instance, zinc nitrate, showed better stability in the neutralized iron or tin solutions, but because of the more expensive nature ofzinc salts, the use of the latter materials is impractical.

The ratio of the aluminum salt to the alkali-metal salt can be varied widely, depending on the particular alkalimetalsalt employed, the aluminum salt used, the conthe aluminum salt isnot deleterious to the stability of the solution nor to the water-repellency properties ofsuch neutralized solutions. However, optimum molar ratios of the ingredients are those described above.

In order that those skilled in the art may better understandhow the present invention may be practiced, the

following examples are given by way of illustration and not by way of limitation. All parts are byweight.

EXAMPLE 1 The sodium salt of methylsilane trial was prepared by hydrolyzingl mol of methyltric'hlorosilane by-iadding it, rapidly with stirring to a large excess of water., The

) solution 4 amount of water present was substantially in excess over that required to effect complete hydrolysis of all the silicon-bonded chlorine in the methyltrichlorosilane.

The resultant solution was allowed to stand until substantially all the methylpolysiloxane had precipitated in the form of a fine powder. This powder was filtered from the remaining solution, washed to remove acid, filtered and dried. The solid gel particles were dissolved by stirring in a 50 per cent, by weight, aqueous sodium hydroxide solution. Generally, 1 mol of the methylpolysiloxane is allowed to react with about 1 to 1.05 mols of sodium hydroxide to give the alkali-metal salt, namely, the sodium salt of methylsilane triol. The resultant alkaline solution had a total solids content of about 4-67 per cent of which about 14.3 per cent was titrated as sodium oxide and contained about 30 per cent methylpolysiloxane solids calculated as CH3SiO1.5. The com position had a specific gravity of about 1.35 to 25 C. and a pH of about 13. This sodium salt of methylsilanetriol (which is also known as sodium methyl siliconate) is believed to have structure I in dilute aqueous solution, and it can be dried to a white solid having the structure II asits molecular formula:

EXAMPLE 2 About 66.6 grams of the sodium methyl siliconate solution prepared in Example 1 was diluted with water to 1000 grams. To this solution was added a sufficient amount of solid aluminum nitrate of the formulation Al(NO3)a.9HzO until the solution was acid to phenolphthalein; 9' grams of additional sodium methyl siliconate solution were added to give a faint pink color with phenolphthalein (pH=8). This neutralized solution which contained 2.2 per cent methyl polysiloxane (calculated as CHzSiOrs) had a molar ratio of 1 mol aluminum nitrate to 3.35. mols of sodium methyl siliconate. The shelf life of this solution was greater than two months.

A neutralized solution of the sodium salt of methyl sila'ne triol containing 4.6 per cent methyl polysiloxane (calculatedas 'CHsSiOLs) was prepared by using an aqueous solution of 3.7 mols sodium methyl siliconate to 1 mol of aluminum nitrate. This particular neutralized solution had a pH of 9.

EXAMPLE 3 This example illustrates another method for preparing the neutralized solutions (that is, solutions of varying pH and lower than the initial sodium methyl siliconate More particularly, 3.75 grams (0.01 mol)- aluminum nitrate nonahydratewere dissolved in 50 ml. water, and 6.6 grams 0.03 mol CHsSiOzNa) of the aqueous sodium methyl siliconate solution prepared as in Example l were also dissolved in 50 ml. water. The two solutions were heated to about C. and thereafter the aluminum nitrate solution was poured into the sodium methylsiliconate solution with stirring to give a clear solution having a pH of about 6.8.

EXAMPLE 4 A portion of the sodium methyl siliconate solution prepared in Exa'mpleglwas diluted with water to give a solution containing 2.1 per cent methyl polysiloxane calculated as CH3SiO1.5. Varying amounts of this solution were added to a, solution composed of 2.82 grams aluminum nitrate nonahydrate dissolved in grams water. The following Table I shows the effect in pH change of adding the sodium methyl siliconate solution to the aluminum nitrate solution. The solution of aluminum nitrate in each instance'contained 0.0074 mol aluminum nitrate nonahydr'ate.

CHaSiOzNa Table I Mols Sodium Math 1 Millilitres Added y siliconate H oeoqoacawmpwwoew All of the solutions prepared in accordance with the above-described procedure using the ratio of ingredients recited in Table I were clear and stable for relatively long periods of time.

EXAMPLE 5 EXAMPLE 6 In this example 38 grams of basic aluminum acetate were added to a solution consisting of 100 grams (0.44 mol CI-IsSiO1.5) sodium methyl siliconate (30 per cent CH3SiO1.5) dissolved in 900 grams water. This gave a solution having a p H of 8 and contained 2.9 per cent by weight thereof. methyl polysiloxane calculated as CHsSiO1.5

This solution was clear and had a shelf life greater than three weeks.

EXAMPLE 7 The aqueous solution of neutralized sodium salt of methylsilane triol (pH=8) prepared in Example 2 which contained the sodium salt in an amount equal to about 2.2 per cent, by weight, the said weight being calculated as CHSSiOLE, was then used to treat common brick by immersing the brick for one minute in the aforesaid solution. The brick was then allowed to air-dry for about 48 hours and then immersed in inch of Water to determine the water pickup after varying intervals of time. A control was also conducted in which a common brick without the prior waterproofing treatment was also immersed in the water to determine the amount of water absorbed. An additional sample of the brick was treated in the same Way With a non-neutralized sodium salt of methylsilane triol solution containing the same amount of methylpolysiloxane calculated as CHsSiO1.s. A still further test was conducted on a neutralized sodium salt methylsilane triol in which instead of air-drying the brick, it was oven-dried at about 125 C. for five minutes. The following Table II shows the results of waterproofing common brick by these various methods.

The sodium salt of methylsilane triol and the neutral ized sodium salt of methylsilane triol (both diluted with water to contain about 1.9 per cent, by weight, of the sodium salt, the said weight being calculated as CH3SlOL5) prepared as in Example 3 were used to treat various textiles by dipping the latter in the solutions of the Water repellent and then air-drying in the case of the sodium methyl siliconate solution and oven-curing the aluminum nitrate neutralized solutions at C. for 5 minutes. Additional samples were used as waterproofing materialsin which the alkali-metal salt of methylsilane triol (in the same weight concentration) was neutralized With acetic acid to a pH of about 7 and textiles treated with these neutralized solutions and air-dried in one case, and in another case the treated textile was heated at 125 C.- for about 5 minutes. After treatment of the various cloths, each cloth was subjected to a water-spray test using the method set forth in the 1945 Year Book of the American Association of Textile Chemists and Colorists, vol. 22, pages 229 to 233. The table below shows the spray rating of various textiles treated in accordance with the procedures described above.

It will, of course, be apparent to those skilled in the art that in making the neutralized compositions herein described, other alkali-metal salts of different hydrocarbon-substituted silane triols may be employed Without departing from the scope of the invention. Thus, instead of usin sodium salts of methylsilane triols, other salts, for example, potassium, lithium, cesium, etc., salts of the methylsilane triol may be used without departing from the scope of the invention. In addition, it Will also be apparent that the invention is not limited to the particular organosilane triols described in the foregoing examples, but other hydrocarbon-substituted silane triol salts may be employed as, for example, the metallic salts of phenylsilane triol (which may be prepared by hydrolyzing phenyltrichlorosilane and dissolving the hydrolysis product in a strong inorganic base), ethylsilane triol, benzylsilane triol, tolylsilane triol, etc.., salts. It is also to be understood that the particular concentrations of the alkali-metal salts in water described above prior to neutralization are not intended to be limiting and lower or higher concentrations of such alkali-metal salts may be employed Within the scope of the invention. Finally, it should be noted that the particular water-soluble single aluminum salt employed may also be varied as long as it maintains the stability of the solution without causing undesirable precipitation or gelation. Obviously, the concentration of the aluminum salt added to the alkali-metal salt for neutralization purposes may be varied within wide limits depending, as pointed out above, on the type of alkali-metal salt employed, the specific aluminum salt used for the purpose, the degree of neutralization desired, etc.

The compositions herein defined are eminently suitable for rendering water-repellent all kinds of solid bodies including textiles, paper, porcelain, glass, ceramics, and various types of masonry, for instance, concrete, gypsum, etc. In rendering textiles and paper Water-repellent, the disadvantage of weakening the paper or cloth, Which is inherent in the use of the alkali-metal salts, is materially obviated so that no diiference in the strength of the paper tqxti s is apna entbeiore or after treatm nt i h; the qu r lized -m .ta1 a1 What I c as new; and desire to secure by Letters Patent gof; the United States; is:

1-, A- stable solutionhaving a pH of from 6.8 to 10 comprising the product oi reaction in an aqueous medium of. ('1) anaqueous solution of; an alkali-metal salt of impairingthestability. of the latter, there being present from 0.001 to 0.4mol of the aluminum salt for each mol of; the alkali mctal salt of the methyl silanetriol.

2. A stable solution having a pH of from 6.8. to 10 comprising the product of reaction in an aqueous medium of (1) an aqueous solution of a Water-soluble alkalimetal salt of methyl silanetriol having the formula wherein the concentration in the aqueous solution ofthe alkali-metal salt when calculated as CHsSiO1.5 is less than 6%, by Weight, and (2) aluminum nitrate which is present in an amount equal to from 0.001 to 0.4 mol of the latter for each mol ofthe aforesaid sodium salt.

3. A stable solution having-gag pH of from 6.8 to 10 comprising the product of reaction in an aqueous medium of (l a water-soluble alkali-metal salt of methyl silanetriol having the-formula wherein the concentration in the aqueous solution of the alkali-metal salt When calculated as CH3SiO1.5 is less than 6%, by weight, and (2) aluminum sulfate which is present in an amount equal to from. 0.001 to 0.4 mol for each mol of the sodium salt.

4. A stable solution having a pH- of from 6.8 to 10 comprising the product of reaction in an aqueous medium of (1) an aqueous, solution of a sodium salt of methyl silanetriol having the formula OH 3HaS i -ON11 wherein the'concentration in the aqueous solution of the latter sodium salti'when calculated as'CHsSiO1.5 is less than 6%; by'weight and (2) aluminum nitrate, there beings present from- 0:0,01' to (M mol of the aluminum nitrate'ror each mol of? the sodium salt of the methyl silanetriol;

References Cited intthe-file of this patent UNITED STATES PATENTS 2,438,055 Hydeetal. Mar. 16, 1948 2,507,200 Elliottet al May 9; 1950 a 

1. A STABLE SOLUTION HAVING A PH OF FROM 6.8 TO 10 COMPRISING THE PRODUCT OF REACTION IN AN AQUEOUS MEDIUM OF (1) AN AQUEOUS SOLUTION OF AN ALKALI-METAL SALT OF METHYL SILANETRIOL HAVING THE FORMULA 